let str = "border-left-color"
let str1 = str.split(/-/, 3)
console.log(str1);
for (let i = 1; i < str1.length; i++) {
    let a = str1[i].match(/\w/)
    let c = a[0].toUpperCase()
    str1[i] = str1[i].replace(/\w/, c)
}
console.log(str1.join(''));